U.S. Pat. No. 5,270,610, Schoenherr et al., the disclosure of which is hereby incorporated by reference, describes a double-ended, single-based electric lamp. The vitreous bulb of the lamp is formed with a tubular extension which is melt-sealed within a holder portion. The holder portion is adjustable to adjust the position of the bulb with respect to the base, so that, when the base is secured to, or within a reflector, the position of the lamp can be properly adjusted for desired optical characteristics of the lamp-reflector combination. The light source itself is formed as a single-based high-pressure discharge lamp especially suitable for automotive applications; the lamp bulb or lamp vessel, and the discharge vessel or portion of the lamp, are especially suited for automotive use. This lamp does not have an outer envelope which reduces ultraviolet (UV) radiation emitted from the lamp during operation thereof.
International Application PCT/DE94/00600, published as WO 94/28576 (United States designated), Wittig, et al., assigned to the assignee of the present application, describes a high-pressure discharge lamp and, especially, a single-based high-pressure discharge lamp particularly adapted for use in an automotive headlight. The lamp has a double-ended sealed discharge vessel surrounded by an outer envelope or shroud. The outer envelope is melt-sealed to the discharge lamp itself in the region of pinch seals of the discharge vessel, and positioned outside of the base. The base-adjacent end of the discharge vessel is formed with a tubular extension similar to the lamp described in connection with the above referred to reference U.S. Pat. No. 5,270,610, Schoenherr et al., which, in turn, is melted into an adjustable holder portion within the base.
It has been found that the relatively thin tubular extension in the region between the outer envelope and the base might fracture when the lamp is subjected to shock or vibration.
European Published Application EP 0 321 866 A2, Gaugel, assigned to the assignee of the present application, discloses a single-based high-pressure discharge lamp, particularly suitable for automotive headlights, having a double-ended discharge vessel and a double-ended sealed outer envelope or shroud. The shroud completely encloses the discharge vessel. The current supply leads to the discharge vessel pass through pinch-sealed ends of the shroud. The end of the outer envelope or shroud close to the base is supported by a metallic holder which, in turn, is located within a plastic base sleeve, and secured therein. It has been found that assembly of the outer envelope or shroud within the base, and attaching the discharge vessel within the envelope or shroud, is comparatively expensive and would unduly increase the cost of a mass-production item.